AS the proportion of elderly in the U.S. population increases, the importance of understanding the molecular mechanisms of aging is penultimate. The liver, unique in its ability to regenerate, has diminished capacity to repopulate its cells with age. The effects of the exposure to toxic chemicals, and the increased use of medications by the elderly may be exacerbated by the age-related impairment of the ability of the liver to replenish cells. We have recently shown an age-dependent decline in hepatocytes of a very early step in the signal transduction pathway in response to a mitogen. This suggests that there are age-dependent changes in basal expression of EGF receptor pathway regulatory genes in the unstimulated hepatocytes. We propose to determine age-related changes in basal expression in the liver using the technique of serial analysis of gene expression (SAGE). This powerful technique utilizes a high efficiency of sequence-based analysis to determine the full array of genes expressed within a cell. Furthermore, advanced software analysis will allow us to identify statistically significant alterations in expression of both novel genes, as well as previously reported genes, in young and old hepatocytes. Candidate genes identified by SAGE will be confirmed by northern blot analysis for changes in expression during aging. Candidate regulatory genes of the EGF receptor pathway (i.e. kinases and phosphatases) will be additionally screened by expression in transient transfection assays to confirm effects on EGF receptor-induced signaling. It is almost certain that SAGE analysis will identify potential changes in liver gene expression during aging. Additionally, the focused molecular and biochemical analysis of candidate genes will provide a powerful and selective screen for future understanding of age-dependent changes in liver function.